Program transmission over wires



Feb. 3, 1925. 1,525,053

'J. F. TOQMEY PROGRAM TRANSMISSION OVER WIRES Filed Nov. ll. 1922 INVENTOR Patented Feb. 3, 1925.

UNITED STATES PATENT- OFFICE; 1

JOHN F. TOOMEY, on NEW Y RI 'N. Y., AssIeNoR TOAMERICAN TELEPHONE-AND TELEGRAPH-COMPANY, A CORPORATION or NEW YORK.

PROGRAM TRANSMISSION OVER WIRES.

Application filed November 11, 1922. Serial No. 600,359.-

tems for disseminating news, information,

music or the like.

Various schemes'have been proposed heretofore for program transmission purposes. The only one ofthese schemes which has been exploited to any extent is radio broadcasting, that is the dissemination of news, information or entertainment by means of radio telephone equipment so that persons provided with suitable radio receiving sets tuned to the proper wave length may receive.

the distributed entertainment or the like.

I his method, however, has very serious objections. In the first place, numerous broadcasting stations in the same area operate on wave lengths sufiiciently close together to interfere with each other. Furthermore. radio telephonic transmission necessarilyin'volves the use .of a much wider.

band of the frequency spectrum than is used for wireless telegraph purposes, and 1n view of the fact that the number of wave lengths available for radio communication are nec-' essarily limited it is undesirable t'hatwave lengths necessary for commercial communication should be utilized for purposes of mere entertainment. Finally, in order to avail himself of the transmitted information or entertainment, each individual subscriber must. provide himself with a radio receiving equipment which involves storing upon his premises expensive storage batteries which are constantly in need of recharging, together with a considerable amount of delicate and elaborate electrical apparatus, such as coils, detectors, amp-lifiers, etc., all of which involve careful maintenance. as now'known is, at its best, an inherently ugly thing, absolutely out of place in the home and requiring for its operation a network of unsightly wiring.

Realizing the inherent limitations of,

radio broadcasting, proposals have been made to use existing wire systems, such as telephone,'telegraph or power networks for Moreover, the radio receiving set program transmission purposes by transmitting carrier. frequencies over such existingpower or communication lines. Such methods, however, as have been heretofore proposed along this line have involved somewhat complicated and expensive appa ratuf owing to the use of filters for separating he ordinary voice frequencies from the carrier frequencies. In accordance with the present invention, however, it is proposed to overome this difiicultyin systems of this character by transmitting thetarrier frequency on which the program is superposed overt-he two sides of the line in parallel.

The invention may now be more fully understood by reference to the following detailed description thereof when read in connection with the accompanying drawing, the

figure of which shows a circuit arrangement illustrating the priniples of the invention.

Referring to the drawing, L designates an ordinary telephone subscribers line terminating at one end at a subscribers station A and at the other end in a central oifice At the station A, the usual form of telephone set 10 is provided for ordinary telephonic purposes. A bridge 30, tuned to the carrier fre uency used for transmission, is also provide midpoint of the bridge a connection 31 is extended to ground through the-contacts of a .key K, by which-the program connection may be controlled at the subscribers station. A detector 32-is associa-ted'with the ground tap 31through a transformer 14,- and an amplifier 33 isconnected be: tween the output of the detector 32 and the loud speaking receiver 11.

At the central station'B, the usual type of switching jack J is provided but in order .to provide a ground tap 34 at the central station for the purpose of superposing the carrier frequencies on the line L a transat the substation and at-the.v

former 35 is interposed between the line L and the jack J. The usual line relay LR is connected with the line winding of the transformer 35 and controls the circuit of. a

line lamp 15.,over the contacts of the usual as is usually the case, but its contacts are so arranged that when actuated the cut-off relay opens a circuit of the line lamp and is tuned to the carrier frequency used for program transmission and is connected through a transformer 37 to a circuit leading to a program. station D. A modulator 38 is provided for modulating the carrier frequency in accordance with the program currents and an amplifier 39 is also provided for amplifying the program carrier frequencies impressed upon the circuit 34:.

The operation isas follows: when the circuit is to be used for ordinary telephone purposes, the contact of the key K is open and the subscriber, by taking down the receiver, energizes the line relay LR, which completes acircuit for the line lamp 15 over the contacts of the cut-off relay'COR. The operator, in answering the call by inserting a plug in the jack J, operates the cut-off relay COR,which opens the circuit of the line lamp and completesa circuit for the supervisory apparatus of the cord circuit. from the tip of the jack J to the upper winding of the transformer 35, over the left-hand front contact of the cut-off relay COR, ri ht-hand front contact of the line relay Li right-hand front contact of the cut-off relay COR, through the resistance 36fand lower winding of the transformer 35 to the ring of the jack J. This circuit maintains switchhook control over the supervisory apparatus of the cord circuit so that when the subscriber hangs up his receiver at the end of the conversation the line relay LR is deenergized and the circuit just traced is opened,;thereby giving the disconnect signal.

Either while the line is being used for ordinary telephone purposes or when it is not so used, a program circuit may be established over the line by closing key K, thereby connecting the midpoint of the bridge 30 to ground through the transformer 14. The program currents from the station D modulate the carrier frequency supp-1y to the modulator 38 and the amplified carrier is transm tted through the transformer 37 and over-the two sides of the line L in parallel and thence to ground over the ground tap 31. The carrier frequencies thus transmit-ted over the line do not actuate the subscribers set as the subscribers set 10 is connected to equal potential points of the two sides of the line with respect to the carrier currents. The carrier currents received in the circuit 31 are detected by the detector 32 and after being suitably. amplified with the amplifier 33, actuate the loud speaker 11 so that the information, music or news transmitted from the station D may be heard in said receiver. The loud speaking set at the station A may be also used to receive broadcasting the spirit of the invention as from a radio broadcasting station. This may be done by tuning the circuit of the detector -32 to the frequency of the radio station and closing the key K, thereby treating the line L and the ground tap 34: at the'central station as a receivin antenna. If the program station D shoul be in operation, the subscriber may call up the central operator and ask to have the rogram connection to the station D opened y means of the switch 40 so that only the radio broadcasting will be received. It is obvious that the general principles herein disclosed may be embodied in other and different forms without departing from defined in the appended claims. W

What is claimed is:

1. In a telephone system, a telephone line terminating at acentral ofiice at one end and a subscribers station at the other, a telephone set at the subscribers station, a program transmitting station, means to translate currents from said program transmitting station into carrier frequencies, means to transmit said carrier frequencies over the two sides of the line in parallel, a connection at thesubscribers station to receive currents transmitted over the two sides of the line in parallel, a special receiving apparatus at the subscribers station, including means for, translating carrier frequencies into ordinary signaling currents, and an operators position at the central office having switching means whereby said line may be interconnected with other telephone lines for telephonic intercommunication while maintaining the connection to said program transmitting station.

2. In a telephone system, a telephone line terminating at a central-oflice at one end and a subscribers station at the other, a telephone set at the subscribers station, bridge connections across the line at the central office and at the subscribers taps connectedto the mid-points of said bridges, a rogram transmitting station connected wit the ground tap at the central ofties, a special receiving apparatus associated with the ground tap at the subscribers stati on, means at the program transmitting station for translating the program currents into carrier frequencies, means at the subscribers station for translating the carrier frequencies into ordinary signaling frequencies, and an operators position at the central ofiice having switching means whereby said line may be interconnected withother telephone lines for telephonic intercommunication while maintaining the connection to said program transmitting station.

In testimony whereof, I have signed name to this specification this 10th day of November 1922. 7

JOHN F. TOOLEY.

station, ground 

